Lower-value voltage limiter



NOV. 22, B N G LOWER-VALUE VOLTAGE LIMITER Filed Sept. 30, 1963 FIG.

INVENTOR. BERNARD N. GAON ATTORNEY 3,287,567 is a ailf er- LOWER-VALUE VOLTAGE DIMITER Bernard N. Gaon, orange; Calift; a'ssignofito North American Aviationylnc. Filed;Sept.'30,-1963;Ser;N0.312 568 and particularly to a s e wave;

f .J be m si na a a a ed si a nlpha e w in be trans lated to .a load ist cs-;:-i-,.,. v Another object is owe -3 2 1 vq a elim tfl l1 shat istics.

; The e: nda th rao je l l are .aghieved b which a lower value l iniitis". s/et by v an i inputS 5 signal I and;

th H "it; goes below po e fQ mndu tiww iunct on- HA :cur junction to a load; no oth preserve the waveforms of theinput signalgand t nc vo a e, andt t llQ the it heinmit;.s gna 39 low Signal hichilmay tassi m a s, su -a ta s nus. wn es si-tp t e np ts al is provided omprisi a a i oi h st each d des? 7 R a we;s condl qmm dun ttnw iai Pied tssy current limiting resistor to the load onsisti mpedan esummi :netwqtkti e pbja .lt nsizad ant en f, w come apparent from the followin description withreference to the accompanying drawing in whic ha FIG. 1 is a circuit xdi'agram bf an e nib'odiment of the invention; a diagram of the characteristigs of the circuit ni lG l; a M. a r F,I: G 3 ;is a waveform'diagram represent ng th oper ingcharacteristi csofthe cir R eferring now to FIG; "1 the lower value of asiriiis phase sinusoidal references signal E is not allowed to g o a A a regardless of how low 'tli valueofthe input signal e-=' comes, and to wtth 1 si nalwh ai riseaa a e the reference signal. 70

The operation of the circuit can best be understood by reference to the diagram of FIG. 2 which shows the i nal 0112 E s s i i t ate hei out u s al Ed w a mvary a a: in ar fwi qn, 10f Ximt l th i put signal om equa Q-Q s t an, n-

,The r rs u f .11"

fQE GMZ f mo iye val slotX wmpr se ea pa r 0i diodes 10 and 11 having their. rcathodes connected to a qcmmvn iiu o 1A and -the nanq es v. t in cte t ansi hea renc s n l n are p t ve y-j A H.rent. i ntin ist rr flqouplest h t on A- oa mp d nc nsumming,n work cuit p ti n-10f: wh' h pose s h d al 2 r: e ve 1 llies; o ;X: ampus s, iQdesa-IS; andt fiha ing their an des o n ct d a: rbm non j n t on 1 d t h ir :c h destq a E1- ;an the zref r n lsour EL .r spw: se ondrc e t m ng resi or l7vconne,cts the junction B :to ;the 1 impedance: summingv network 13- 9 ha thetcomp sit loutput; s gnal E0 is a linear. function.

J12; Qr i E foruboth positive and, negative values ofv X exceptf W ent i a a func i n? of; X

, qualitov or less han n and; E ;respecti v ely; ,then E visvavgcompos'ite .MO the positive and negative values-of E i 0 n. the illustrated embodiment of ;the;1nvent1on,;,the n- 1:-i. put signal E is an amplitude-modulated:A;Caqsigna1-;tand

i' erating -,characteristics oft-the invention for sinusoidal signalsgp; 1 1. r; 1 JfgEtwocycles 50f he input signalxE shown 1n; FIG. ;3 are; comp aredwith twokcycles; of" the ,reference signal t E the Waveforms A and. Bfiaregproducedwatt the respective the first cycle, when: E is, greater than E ;the'signal at the. 1junct-ionA is as,ill,ustrated: by; theqwaveformrAdurt-f ing the samev periodwwhile the signal atthe junction Btis 0 ,due. to; the positive signals 1 applied ,to ,Ethe; ,cathodes of thesdiddes liand k16; ,Duringqthe secondhhalf ofnthe first;:yc1e,i1thel-signalat thejunction-A drops tO;0, due to the; negativefsignals applied to: the? anodes: of! the diodes 10, andwlll While the signal at athe junction B- follows the reference; :sigriali =E i- Thus, during that :fir'st :cycle, only the diodes 11 and 1 6"conduct during thearespective pQSl:

tive and negative half cycles of therefere'nce signalbE because the reference signal E is -greater than-:the input signalE ::therebyjeversebiasingthediodes. 10 and 15.

- During;-the::first'-half E of .--'the second cycle,: whi1e; -E is greater than E only the :diode r10 conducts,z:all;.other diodes: :..are reverse-biased. The 5 signal ate Ithe ajuncti'on A wilhthen have: the-value of: the. input signal. E as shown in the waveforms of FIG. 3. Similarly; during'theasemnd half aof lithexsccond ncycle onlyathe diode115,-Conductsm It 3, the forward voltage drop of thevconductingdiodes is negle ted, iU E=1.i l-:: I 'Q applications tha v ltage-drop; is negligi le;; as;icompared to the;amplitudehoflithe'l input signal; E tand the; -refer ence1 voltageE I ,1511 .6;o1.,1tputvoltage {E018 zth p iteljorrsuiir f the signals, at; the junctions Aand-B as [shown in EIG For m re p e summ ing lQffl hew ignals-aat th taiuncti n A; and 13,; an op t n l amplifi r with n-at negat v 1f back resistor connected between its output terminal and tseix tr erminal lQaYh=1 l b lFPt twi ht? im n Since only one diode is conducting at any given time,

and there is no other current path to the signal source E or the reference source E the output signal E is not combined with either the input signal E or the reference signal E whichever has the lowest amplitude at the given time. Thus the output signal E faithfully follows the input signal until the lower limits established by the reference signal E is reached; thereafter, the output signal E faithfully follows the reference signal E regardless of how low the input signal E becomes. Accordingly, the advantage of this invention is that there is no distortion of the output signal E Although the foregoing embodiment of the invention is as a single-phase limiter, a dual-phase limiter could be provided by adding a phase detector which controls the phase of the reference signal E in accordance with the phase of the input signal E There are many applications for this invention in control systems where lowervalue limiting is necessary, both single-phase and dualphase. One example of a single-phase application is in an aircraft flight control system where commanding an altitude below a predetermined value would be detrimental. For instance, the input s1gnalE may be an amplitude modulated A.C. command signal for altitude which is to be used by a flight control computer to produce flight control signals for automatically achieving the commanded altitude. The reference signal E may then be an amplitude modulated signal representing an altitude such as 250 feet below which it is not desired to fly the aircraft regardless of what input command signal is applied, An example of a dual phase application is in a control system for hydrofoil marine vessels where E is an amplitude modulated altitude command signal of one phase for greater altitude and of an opposite phase for lesser altitude, and the reference sign-a1 E represents the maximum diving command signal of either phase which the system may carry out without causing the hydrofoils to break out through the surface of the water or the hull to impinge the surface of the water.

While.the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in the art many modifications in structure, arrangement, proportions, the elements, materials, and components, used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operating require ments, without departing from those principles. The appended claims are therefore intended to cover and embrace any such modifications, within the limits only of the true spirit and scope of the invention,

What is claimed is:

1. A lower value voltage limiter comprising one pair of unidirectional conducting devices connected to one common junction, each device having two terminals and being poled for forward conduction in the same direction with respect to said one junction,

a current limiting resistor coupling said common junction to a load,

one of said devices adapted to be connected to an input signal source tending to provide conduction of current therethrough at least part of the time,

and a reference signal source connected to the other of said devices tending to provide current therethrough at least during the time said input signal tends to provide current through said one device, whereby current is provided to said low impedance summing network from said input signal source or said reference signal source, whichever is greater in amplitude.

2. A lower value voltage limiter as defined by claim 1 further comprising a second pair of unidirectional conducting devices connected to a second common junction, each having two terminals and being poled for forward conduction of current in the opposite direction with respect to current through said one pair of devices,

a second current limiting resistor coupling said second common junction to said load, said load comprising a low impedance current summing network,

one device of said second pair having its second terminal connected to said signal source and the other device of said second pair having its second terminal connected to the reference signal source, whereby lower value voltage limiting of either polarity is provided.

3. A lower value voltage limiter as defined by claim 1 wherein said devices comprise junction diodes.

4. A lower value voltage limiter as defined by claim 2 wherein said devices comprise junction diodes.

5. A lower value voltage limiter comprising a pair of diodes having like first terminals connected to a junction,

a resistor coupling said junction to a load,

a second terminal of a first one of said pair of diodes adapted to be connected to a first signal source, and

a second signal source connected to a second terminal of a second one of said pair of diodes, whereby said load receives a sign-a1 at any given time from either said first signal source or said second signal source, whichever is greater in amplitude at said given time.

6. A lower value voltage limiter comprising a first pair of diodes, each having its cathode connected to a first junction,

a second pair of diodes, each having its anode connected to a second junction,

a pair of resistors, each coupling one of said junctions to a common terminal of load,

a first signal source having an output terminal connected to the anode of one of said first pair of diodes and to the cathode of one of said second pair of diodes, and

a second signal source having an output terminal connected to the anode of the other of said first pair of diodes and to the cathode of the other of said second pair of diodes.

7. In an apparatus for limiting the lower value of a voltage signal being translated to a load, the combination comprising diodes associated in pairs,

an alternating input signal source connected respectively to the cathode of a first one of said diodes and to the anode of a second one of said diodes,

a reference signal source connected respectively to the cathode of a third one of said diodes, and to the anode of a fourth one of said diodes,

a first coupling resistor connected in series between the cathodes of said second and fourth diodes and said load, and

a second coupling resistor connected in series between the anodes of said first and third diodes and said load.

References Cited by the Examiner UNITED STATES PATENTS ORIS L. RADER, Primary Examiner.

DDEN, Ass stant Examin r 

1. A LOWER VALUE VOLTAGE LIMITER COMPRISING ONE PAIR OF UNIDIRECTIONAL CONDUCTING DEVICES CONNECTED TO ONE COMMON JUNCTION, EACH DEVICE HAVING TWO TERMINALS AND BEING POLED FOR FORWARD CONDUCTION IN THE SAME DIRECTION WITH RESPECT TO SAID ONE JUNCTION, A CURRENT LIMITING RESISTOR COUPLING SAID COMMON JUNCTION TO A LOAD, ONE OF SAID DEVICES ADAPTED TO BE CONNECTED TO AN INPUT SIGNAL SOURCE TENDING TO PROVIDE CONDUCTION OF CURRENT THERETHROUGH AT LEAST PART OF THE TIME, AND A REFERENCE SIGNAL SOURCE CONNECTED TO THE OTHER OF SAID DEVICES TENDING TO PROVIDE CURRENT THERETHROUGH AT LEAST DURING THE TIME SAID INPUT SIGNAL TENDS TO PROVIDE CURRENT THROUGH SAID ONE DEVICE, WHEREBY CURRENT IS PROVIDED TO SAID LOW IMPEDANCE SUMMING NETWORK FROM SAID INPUT SIGNAL SOURCE OR SAID REFERENCE SIGNAL SOURCE, WHICHEVER IS GREATER IN AMPLITUDE. 